A large body of evidence has indicated that induction of endogenous antioxidative proteins seems to be a reasonable strategy for delaying the progression of cell injury. In our previous study, cilostazol was found to increase the expression of the antioxidant enzyme heme oxygenase-1 (HO-1) in synovial cells. Thus, the present study was undertaken to examine whether cilostazol is able to counteract tumor necrosis factor-Ձ (TNF-Ձ)-induced cell death in endothelial cells via the induction of HO-1 expression. We exposed human umbilical vein endothelial cells (HUVECs) to TNF-Ձ (50 ng/ml), with or without cilostazol (10ՌM). Pretreatment with cilostazol markedly reduced TNF-Ձ-induced viability loss in the HUVECs, which was reversed by zinc protoporphyrine IX (ZnPP), an inhibitor of HO-1. Moreover, cilostazol increased HO-1 protein and mRNA expression. Cilostazol-induced HO-1 induction was markedly attenuated not only by ZnPP but also by copper-protoporphyrin IX (CuPP). In an assay measuring peroxisome proliferator-activated receptor-Ճ (PPAR-Ճ) transcription activity, cilostazol directly increased PPAR-Ճ transcriptional activity which was completely abolished by HO-1 inhibitor. Furthermore, increased PPAR-Ճ activity by cilostazol and rosiglitazone was completely abolished in cells transfected with HO-1 siRNA. Taken together, these results indicate that cilostazol up-regulates HO-1 and protects cells against TNF-Ձ-induced endothelial cytotoxicity via a PPAR-Ճ- dependent pathway.